This invention relates to a magnetic character recognition system and, more particularly, to a document reader system in which a single gap magnetic read head is used for reading magnetized characters embodied in the form of E-13B character font printed on a document.
In single-gap magnetic character reading systems, a single analog input waveform is obtained by passing the characters to be sensed, normally printed on a document, beneath a magnetic read head at least as wide as the height of the characters and having a single flux gap. The signal generated by the read head is a derivative waveform representing the rate of change of magnetic flux traversing the head as the characters are scanned. Since the distribution of ink, and thus flux, associated with each different character is unique, the waveform derived for each different character uniquely identifies that character.
To simplify the timing of the waveform analysis process, the characters are provided with stylized geometric features which impart anticipatable timing characteristics to the derived waveforms. Thus, in accordance with this scheme for reader identification, each character of the E-13B font is divided into a predetermined number of vertical segments corresponding to the location of bar portions of the character. The characters are designed such that the distribution of ink undergoes significant change only at the boundaries between each segment. Hence, peak fluctuations in the derived waveform caused by these variations in ink distribution can occur at only predetermined times during the character scan.
Prior character recognition systems have utilized the amplitudes of each of the peaks of the generated waveform for correlating with known peak amplitude characteristics of each of the E-13B characters to identify the character read. An example of this type of recognition system may be found in U.S. Pat. No. 3,851,309. Critical to this type of recognition system is the timing of the sampling of the waveform for detecting the occurrence of each of the peaks in the waveform. It is well known that in the actual printing of the magnetic character on the document, variations in width of the bar portion of the characters are obtained which affect the peak amplitude of the waveform. Other errors found in the reading of the magnetic characters can be traced to variations in the speed of the document past the read head thereby displacing the peak position of the waveform with respect to the vertical segment in which the peak amplitudes of the reference characters are measured and used in recognizing the unknown character. Prior art recognition systems have been eveloped to compensate for these variations. In U.S. Pat. No. 3,528,058, issued to Bond, each peak in the waveform of the unknown character is sensed for controlling the generation of the next window during which time the next peak of the waveform is to be sensed. In U.S. Pat. No. 3,629,829, issued to Ordower, each peak in the unknown character is integrated over a predetermined time span for generating a value which is used in recognizing the unknown character, which value is not affected by registration or gross distortion of the input waveform. Difficulties arise using these systems in those cases where the peak curve in the waveform of the unknown character are skewed or unsymmetrical. Using the prior art peak detection systems, the timing of windows generated in response to the sensing of the prior peak amplitude fail to completely cover the peak curve resulting in the generation of a value not representing the total area of the peak. In those cases where the distortion of the waveform results in a multi-peak waveform, complex timing circuits are required to select which peak is the required peak for use by the system in generating a peak amplitude value.
It is therefore an object of this invention to provide a character recognition system which generates a high degree of successful recognition operations under present-day operating conditions. It is a further object of this invention to provide a character recognition system which functions independently of the speed of the characters past the read head. It is another object of this invention to provide a character recognition system which minimizes the effects of variation in ink intensity found in the characters that are to be read. It is a still further object of this invention to provide a character recognition system which consists of a smplified system and circuitry which can be installed at a relatively low cost.